1. Technical Field
The present invention relates to a method for operating an actuator and an actuator device, in particular a pressure actuator that is designed to be used in connection with drainage pipes for production of oil and/or gas in an oil and/or gas reservoir.
2. Description of the Related Art
Drainage pipes of the above type are normally divided into a number of sections with one or more inflow restriction devices that regulate the inflow to the drainage pipe.
U.S. Pat. Nos. 4,821,801, 4,858,691 and 4,577,691 and GB patent no. 2169018 describe prior art devices for the extraction of oil or gas in long horizontal and vertical wells. These prior art devices comprise a perforated drainage pipe with, for example, a filter for sand control around the pipe. A major disadvantage of the prior art devices in connection with oil and/or gas production in highly permeable geological formations is that the pressure in the drainage pipe increases exponentially in the upstream direction as a consequence of flow friction in the pipe. As the pressure difference between the reservoir and the drainage pipe decreases upstream as a consequence of this, the inflow quantity of oil and/or gas from the reservoir to the drainage pipe will also decrease accordingly. The total oil and/or gas production will therefore be low with such a solution. For thin oil zones and high permeability in the geological formation, there is a high risk of coning, i.e. inflow of undesired water or gas into the drainage pipe downstream, where the speed of the oil flow from the reservoir to the pipe is greatest. To avoid such coning, production must therefore be reduced further.
Somewhat higher production than with the above prior art solutions is achieved using the Stinger method, which is discussed in Norwegian patent application no. 902544. This method consists of two drainage pipes, of which an outer one is perforated, and an inner pipe (Stinger), which does not include perforations, extends into the outer pipe to a desired position. The pressure profile and thus the productivity of the Stinger method is somewhat better than for other prior art methods. In thin oil zones with high permeability, however, coning of undesired water or gas may also occur with this method with reduced productivity as a result.
World Oil, vol. 212, N. 11 (11/91), pages 23-78, describes a method of dividing a drainage pipe into sections with one or more inflow restriction devices in the form of displaceable sleeves or throttle devices. However, this publication is mainly concerned with inflow control to restrict inflow from zones upstream in the pipe to prevent water and gas coning.
WO-A-9208875 shows a horizontal production pipe comprising a number of production zones, each of which is connected to mixing chambers that have a greater internal diameter than the production zones. The production zones comprise an external perforated pipe, which may be regarded as a filter. However, the sequence of sections that have different diameters is unfortunate as they create flow turbulence through the pipe and prevent the use of equipment that is normally introduced by means of downhole tractors or “coiled tubing” systems.
The technology for drilling horizontal wells was known back in 1920, but many today still regard it as pioneering technology. In the last twenty years, development work has taken place that allows horizontal wells to be drilled in a safe, effective manner. The current status of technology is that drilling safety is high, and the costs are approximately 50% higher than for vertical wells, but horizontal wells produce three to four times the quantity, depending on the characteristics of the reservoir.
or inflow control device are achieved by utilizing the osmotic pressure difference between the solution in the cell and the external fluid flow or fluid reservoir in relation to the cell.
The actuator in accordance with the present invention is further characterized in that the actuator comprises an osmotic cell that is designed to be placed in the fluid flow, whereby the necessary force and motion for the actuator to drive or adjust a valve or inflow control device are achieved by utilizing the osmotic pressure difference between the solution in the cell and the external fluid flow or fluid reservoir in relation to the cell.